1. Field of the Invention
This invention relates to improvements in the explosion-initiating method for fixing tubes on a tube plate by means of explosives.
2. Description of the Prior Art
There is a demand for effecting connection of tubes with a tube plate in a variety of industrial fields. One of the fields is the production of heat exchangers in which a multitude of tubes arranged in parallel are fixed at their ends on a tube plate extending perpendicular to the longitudinal direction of the tube. Coupling areas between the tube ends and the tube plate should be leak resistant to avoid mixing of materials passing through the heat exchanger.
Methods known for connecting a tube with a tube plate include mechanical expansion of the tube by means of a tube expander followed by sealing of the joint between the tube and the tube plate utilizing gas or arc welding. It is difficult to effect sealing without decreasing the maximum strength of the tube, the walls of which are normally quite thin. Moreover, the sealed joint is often so frigile that it will not resist large changes in pressure. Additionally, the formation of the joint by expansion requires precise controls of the shape, size, and finishing of the hole in the tube plate receiving the tube. For best results, the tube expander must be carefully placed on the tube plate and the expansion must be conducted carefully. The construction of the joint portion by expansion requires a considerable period of time because the portion to be joined should be deformed slowly and, to minimize undesirable stress distribution. Welding of the joint portion may be complicated by limited compatibility between the metals in the tube and the tube plate. In some cases, welding causes permanent softening and annealing of the tube. Minute variations in thickness of the tube in the area to be welded will reduce the reliability of the weld, and often result in leakages.
In order to overcome these disadvantages, explosive tube expansion has been adopted. This technique involves fixing of the tube on the tube plate utilizing explosive energy. The explosion is usually initiated by electric ignition. However, in this procedure, as the number of tubes to be expanded increases, the number of the tubes to be expanded is increased the wiring techniques become more and more complicated, and the time required for wiring increases. This reduces the efficiency of the procedure.